A multidisciplinary approach is proposed to study the teratogenic effects of the methylcarbamate and organophosphate insecticides in the chick embryo. Drug-induced alterations of embryonic development will be examined: 1. in embryos from 0-3 days old, by histological analysis, 2. in developing limb buds, with resepct to cartilage, muscle cholinergic and vascular tissues, and 3. in limb bud cell or organ cultures. Teratogenic effects will also be examined with respect to changes in DNA and RNA species. The observed teratogenesis will be related to two possible mechanisms of the cholinergic insecticides by studying: 1. the alteration of chromatin content due to lowering of NAD levels, and 2. the anti-cholinergic nervous system. These studies will allow us to focus more clearly on the biochemical mechanisms underlying insecticide-induced teratogenesis.